Single-phase induction motors are widely used, due to their simplicity, strength and high performance. They are generally found in household appliances, such as refrigerators, freezers, air conditioners, hermetic compressors, washing machines, pumps, fans, as well as in some industrial applications.
The known induction motors are usually provided with a cage type rotor and a coiled stator, having two windings, one for the running coil and the other for the starting coil. During the normal operation of the compressor, the running coil is supplied by an alternate voltage and the starting coil is temporarily supplied at the beginning of the starting operation, creating a turning magnetic field in the air gap of the stator, a necessary condition to accelerate the rotor and promote motor starting.
This turning magnetic field may be obtained by supplying the starting coil with a current that is time-displaced in relation to the current flowing in the main coil, preferably at an angle close to 90 degrees. This time-displacement between the current flowing in both coils is achieved by constructive characteristics of the coils, or by installing an external impedance in series with one of the coils, but generally in series with the starting coil. The value of this current flowing in the starting coil during the starting process of the motor is generally high, being necessary to use a type of switch for interrupting this current after the time required for promoting the acceleration of the motor has elapsed.
In motors in which a very high efficiency is required, this starting coil is not completely disconnected after the starting period has elapsed, and a capacitor, namely a running capacitor, is maintained connected in series with said starting coil, providing enough current to increase the maximum torque and efficiency of the motor.
For motors with this configuration using a permanent impedance in series with the starting coil during the normal operation of the motor, some starting devices of the PTC or electronic types are known, as described in U.S. Pat. No. 5,051,681.
Other constitutive component of the known starting and protection modules for the electric motors is the thermal protector, which has the function to protect the electric motor in short circuit or overload conditions. This component may be mounted directly to an energizing pin of the compressor or lodged next to it, and connected to said compressor by electric conductors, or also installed in the interior of the compressor, in contact, for example, with the windings of the electric motor.
In some known constructions for a starting system, the latter comprises a module, which lodges therewithin a starting device and a motor protector, and externally carries at least one capacitor, the running capacitor, which is affixed to this module through a capacitor support (U.S. Pat. No. 5,170,307), or directly to said module (U.S. Pat. No. 5,729,416).
In other known constructions, the starting system either dispenses the use of capacitors, or allows the running capacitor (and also the starting capacitor, if provided) to be operatively coupled to the module of said starting system by adequate connecting cables (WO98/21735).
In the constructions in which the running capacitor is affixed to the module of the starting system, directly thereto or through the support, there is provided a fixed or removable rod, having a pin at its free end to receive an engaging portion of the running capacitor. In the solution of U.S. Pat. No. 5,729,416, the end of the fixation rod of the running capacitor is provided with lateral grooves, so as to immobilize the capacitor attached to the module of the starting system. Nevertheless, these grooves do not prevent the involuntary displacement of the running capacitor from its engaging position in relation to the module, since said grooves do not provide axial retention thereto.
Although the known module solutions of starting systems represent a simplification in the assembly of the starting and the protecting elements of the electric motor of compressors, such known systems present the disadvantage of not being sufficiently versatile to allow their adaptation to different configurations and applications for the starting system of an electric motor, requiring, for each variety, a starting system with proper specifications. In the solution proposed in U.S. Pat. No. 5,729,416, the constructive arrangement comprises a shell, which is formed by a basic body lodging a starting device and a thermal protector, which is completely and definitively closed during manufacture, requiring a specific construction as a function of the application to be given to the starting system. Thus, after leaving the assembly lines, the constructive arrangement object of U.S. Pat. No. 5,729,416 does not allow the rearrangement of the components, since the shell is entirely closed, enclosing therewithin the starting device and the thermal protector used in the manufacture. This constructive characteristic forces the customer of the electric motor to store different types of modules directed to different applications. If, for example, a problem occurs in the thermal protector, the whole module must be replaced, spoiling the starting device. The same is true if the defect occurs in the starting device. Furthermore, since the cover is designed to close the whole basic body of the shell, it is not possible to replace any of the components defined by the starting device and the thermal protector.
Another characteristic of the known constructive arrangements is that, in case an insulating protection is required to prevent the user from accessing the supply terminals of the module, the shell is constructed with a specific design, in order to incorporate a double tubular extension, involving the openings for the supply terminals. For this purpose, it is necessary to duplicate the number of tools for manufacturing the different types of shells, increasing costs and reducing the productivity during manufacture, besides increasing the number of stored items.